In [1]}, the authors proposed a semi-definite relaxation based alternating minimization (SDR-AltMin) algorithm to jointly design the digital and analog precoders. In [2]}, the authors generalized SDR-AltMin algorithm to the hybrid SSM system, and proposed two precoders which maximized approximate SR (ASR) based on gradient method and alternating direction method of multipliers respectively. Figure. REF  shows that the proposed two methods in [2]} harvested higher SR performance than the generalized SDR-AltMin method. For hybrid generalized SSM systems, the authors in [4]} proposed a novel algorithm to separately optimize the analog precoder and the digital precoder to maximize SR. As the objective function is non-concave, the authors conceived a pair of concave objective functions to optimize the analog precoder and digital precoder.
<FIGURE>